This invention relates to an actuator mechanism for providing high torque for seating and unseating a valve or the like. The mechanisms further provide a steady closing force against the valve stem to prevent the valve from opening in the event of surging.
U.S. Pat. No. 5,542,643 to Breth discloses a ball valve that is seated and unseated by means of a hydraulic actuator. The piston rod of the actuator is coupled to the lever arm of the valve by a plate. The plate contains slotted holes that permit the plate to be adjustably positioned between the valve lever arm and the piston rod of the actuator. Sufficient adjustment is provided so that the valve can be accurately positioned by the actuator between a fully closed and a fully opened position.
Collins, U.S. Pat. No. 5,078,180, further describes a hydraulically actuated gate valve. The actuator is again connected to the crank arm of the valve by means of plate-like linkage. The valve is opened and closed through the linkage as the piston rod of the hydraulic actuator is extended or retracted.
Although the prior art device provides additional torque for seating and unseating a valve, they are incapable of holding the valve closed when the valve experiences high internal surge pressures. Most valve actuators can seat and unseat a valve under normal conditions. However, they cannot also function simultaneously to lock the valve in a closed position. Additionally, many of these prior art devices close at a relatively high speed causing undue wear and breakage of the valve components.